The invention relates to a method of dewatering the froth fines or flotation concentrates obtained during coal dressing or separation by means of a discontinuously operating sieve scraping centrifuge.
By the dewatering of the froth fines, it is desired to obtain waste water with a low solids content as well as a solid capable of transportation in a noncaking condition.
To this end, there have been employed discontinuously operating scraping centrifuges (magazine "Gluck auf", 1969, pages 1135-1146, especially page 1139, right-hand column, first paragraph). Such centrifuges could not achieve wide acceptance because of the high content of solids in the liquid discharge. According to the numerical tables 1 and 2 on pages 1141 and 1142 of the above-mentioned publication, the contents of solids in the discharge amounts to between 42 and 60 grams per liter. As a result of this high solids content, the discharge had to be supplementally treated in filters, substantially increasing the total costs per metric ton of treating the froth fines. This could also be the reason why the profession turned away from the centrifugal dewatering and turned to exclusive filtration dewatering (see page 1142, left-hand column, right paragraph of the above-mentioned publication). Also, up to the present (see the magazine "Gluck auf" 1976, pages 385-387 and especially page 385, left-hand column, third paragraph), the filtration dewatering has been generally considered advantageous than the contrifugal dewatering both with respect to the solids content in the discharge as well as in operating costs. Thus, the costs for the mechanical dewatering of the froth fines to a residual moistness of approximately 27% with the utilization of vacuum rotating filters are about 2.50 DM per metric ton. The solids concentration in the discharge achieved thereby is between 15 and 20 grams per liter.